1. Field of the Invention
This invention relates to automatic welding equipment and more particularly to welders for seal welding a plug in a tube of the steam generator in a nuclear power plant.
The plugs are placed in leaky tubes in the primary side of the steam generator which has sufficiently high levels of radioactivity to limit the time a workman is allowed therein. One particular important consideration in performing work in a radioactive environment is a wise use of manpower. The objective being to obtain the most effective use of manpower in order to expose each workman to a minimum amount of radiation. This is especially important when the workman is a skilled craftman such as a qualified welder. In cases where the radioactive level has been high, the process of welding one plug in a tubesheet exposed the qualified welder to his allotted quantum of radiation. The apparatus described hereinafter allows a qualified welder to set the proper parameters on the welding torch and plug outside of the radioactive environment. The plug and spindle are removed from the apparatus, allowing an unskilled laborer having a minimum amount of training to enter the radioactive environment, drive the plug into the proper tube and quickly attach the apparatus thereto. The qualified welder can then remotely perform the seal weld. The apparatus described herein not only reduces the time in which a workman is exposed to radiation for each weld, but also practically eliminates all exposure to the skilled qualified welder and thereby greatly increases his availability and productivity. And it also allows the use of unskilled laborers with a minimum amount of training to set up the welding procedure greatly increasing the number of available workmen, each of which may be safely subjected to an allowed quantum of radioactivity.
2. Description of the Prior Art
U.S. Pat. No. 4,103,140 issued in the name of this inventor and a continuation of the Patent Application filed Mar. 8, 1977 in the name of this inventor and assigned Ser. Nos. 775,675 and 775,676 when originally filed and Ser. No. 908,046 when refiled Apr. 18, 1979 show apparatus which is installed in the head of a steam generator to remotely position a tool so that it can operate on tube ends within a portion of the head. The tool is remotely operated driving a plug into a leaky hole and seal welding it into the tube. These tools find application where there are a large number of tubes to be plugged as the time required to set up the tool inside the head of the steam generator is great.
U.S. Pat. No. 4,004,125 sets forth a multi-head welding gun for seal welding tubes to a tubesheet, but does not show a detachable spindle which can be affixed to the plug.